1. Field of the Invention
The present invention relates to a lens barrel provided in an image pickup apparatus such as a film camera or a digital camera, and an image pickup apparatus having the lens barrel.
2. Description of the Related Art
Some of this type of conventional lens barrels have a zoom mechanism that causes a cam cylinder to move a plurality of lens holding frames holding a plurality of lenses along an optical axis while causing a rotation restriction cylinder to restrict movement of the lens holding frames in a rotational direction so as to move the lenses to predetermined positions.
Incidentally, with recent demand for higher shooting magnification, a lens barrel tends to be large due to an increase in the number of lens groups and an increase in the length of the lens barrel in its fully extended state. On the other hand, there has also been demand for slimming down of a camera, and the thickness of a camera with a lens barrel retracted therein has been required to be reduced to a minimum.
For slimming down of a camera, it can be envisaged to reduce the size of barrel members in the direction of the optical axis and connect the lens barrels together in a multistage configuration, but arranging a plurality of cams without crossing them is difficult due to many restrictions.
Moreover, the distance traveled by inner lens groups in the lens barrel along the optical axis tends to increase depending on a design of a lens optical system, and it is becoming very difficult for the cam cylinder to cover strokes of the inner lens groups.
Accordingly, there has been proposed the technique that, to ensure movement of inner lens groups in a lens barrel on the optical axis, a lens barrel train extending toward an image plane is additionally provided inside a typical cam cylinder so as to extend strokes of the inner lens groups toward the image plane (Japanese Laid-Open Patent Publication (Kokai) No. 2007-219435).
According to the technique disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2007-219435, increased shooting magnification and slimming down of an image pickup apparatus can be realized, but because a plurality of barrel members are required to be provided inside the lens barrel, and hence the diameter of the lens barrel, and drive load and optical accuracy error in moving the lens barrel along the optical axis are increased.